Thermal control fuses



No?. 27, 1956 L Po'r'r 2,772,333

THERMAL CONTROL. Fuss United States Patent() THERMAL CONTROL FUSES Leslie Pott, Heaton Norris, Stockport, England Application December 3, 1954, Serial No. 472,967

Claims priority, application Great Britain December 15, 1953 7 Claims. (Cl. 200-117) This invention relates to fuses for protecting apparatus against excessive electric current or against excessive heat.

The invention provides a thermal control fuse adapted for intercalation in an electric circuit characterised in that the fuse element is maintained in a state of tension which may be adjusted to suit any fuse material, and is adapted to be fractured when subjected to a temperature within the solidus-liquidus range of the fuse material whereby to break the electric circuit, which temperature may in certain applications be due to excess electric current through the circuit, or in another application, due to excess external heat.

The improved thermal control fuse is further characterised in that there are no mounting limitations.

According to the invention the improved thermal control fuse comprises a casing, electrical terminals housed in said casing, and insulated therefrom, a basal member attached to said casing, a tubular metal sheath attached to said basal member and furnished within an insulator member having holes for the passage of two terminal wires, and a fuse cartridge connectible to said sheath and housing a fuse element under tension, said terminal wires being in connection at one end to the said terminals and at the opposite end to said fuse element.

In a preferred form the improved thermal control fuse includes a casing housing electrical terminals mounted on an insulated block, said casing being furnished with a basal member provided with a tubular metal sheath in which is located an insulator member having holes for the passage of two terminal wires, the upper ends of which project into the said casing and are connected to the respective terminals, while the lower ends extend through the said insulator member, a further sheath connectible to the first-mentioned sheath and housing continuations of the insulation member and terminal wires and being furnished with a liner, r distance piece, located between the underside of the insulation member and an insert stop secured to the outer end of said second sheath, a fuse secured across the ends of the terminal Wires in such manner that the said terminal wires are held in tension whereby the said fuse is subjected to a predetermined tensile stress.

When the predetermined temperature is reached the fuse melts and the resultant fracture causes the terminal wires to spring apart and so break the electric circuit.

The second-mentioned sheath, hereinafter referred to as the fuse cartridge, is then removed and a fresh fuse is fitted, when the cartridge is again attached.

ln a modification, instead of a removable fuse cartridge, the improved thermal control fuse may have an extended insulation member and the terminal wires may be continuous and project through the said insulation member into the lower sheath, the ends of the 4terminal wires being fitted with a fuse element as before.

The invention Will now be described with the aid of the accompanying drawings, in which Fig. l is a vertical sectional View of a thermal control fuse constructed acice cording to a preferred form of the invention; Fig. 2 is a plan of the fuse shown in Fig. 1 with the cover removed; Fig. 3 is a fragmentary sectional view of a modified form of the invention.

The same reference numerals are used to indicate corresponding parts in the several figures of the drawings.

Referring to Figs. 1 and 2 of the drawings, 10 indicates a cylindrical metal casing furnished with a cover 11 formed with an aperture 13 for passage of electric lead wires; 14 indicates a metal sheath having a ange 15 adapted to form the base of the casing 10; 16 indicates an insulation block housed in the casing 10 and secured to the flange 15 by screws and nuts indicated at 17; 18, 19 indicate gaskets Irespectively interposed between the underside of the block 16 and the flange 1,5, and between the upper surface of the block 16 and a metal plate 20; 21, 22 respectively indicate two terminals each bolted to the plate 20 by screw-bolts 23, 24 and insulated therefrom, the heads of the screw-bolts 23, 24 being located in a recess 25 formed in the base of the block 16.

The plate 20 is formed with a central vertical pillar 26 to which the cover 11 is secured, as by a screw 27; 2S indicates an insulation member or core located within the sheath 14 and formed with holes for the passage of two terminal wires 29, 30 respectively, secured in electrical connection with the terminals 21, 22 by the bolts 23, 24, the ends of the terminal Wires being clamped between the adjacent heads of the terminal bolts 23, 24 and washers 31, 32 strung on said bolts and housed in recesses in the insulator block 16.

An internally screw-threaded union nut 33 is strung on the sheath 14, after which a flanged bush 34 is secured to the lower extremity of the sheath 14, as by welding, the ange 35 of the bush 34 retaining the union nut 33 captive on the sheath 14, see Fig. l. The flange 34 is formed in its face with radially spaced holes or recesses indicated at 36.

37 indicates a detachable fuse holder, for convenience referred to as a cartridge, comprised of a cylindrical metal sheath 38 provided at its upper end with an insulation member 39 fitted in the mouth of the sheath 38 and having two holes therethrough to receive two terminal wires, 40, 41, which project beyond the upper face of the member 39, the end of each terminal wire 40, 41 being reduced in diameter to provide attachment for small springs, respectively indicated at 42, 43.

The terminal wires 40, 41 are each secured in the insulation member 39 by suitable means, e. g., a peg or the like, as indicated at 44, 45.

The terminal wires 4d, 41 project through the bottom of the insulation member 39 to a point adjacent to the open end of the sheath 3S, where the ends of the said terminal wires are drawn together and fastened in such position by a fuse 46. Due to their springy nature the terminal wires 40, 4l are thus held in tension whereby the fuse 46 is subjected to a predetermined tensile stress.

The length of the extending portions of the terminal wires 40, 41 is determined by the degree of tension required to be exerted by the terminal wires when in tensed position.

47 indicates a liner, or distance piece, secured in the sheath 38 between the underside of the insulation member 39 and a thimble insert 48 secured in the lower end of the sheath 38, as by welding. The sheath 38 is furnished at its upper end with a anged bush 49, welded thereto, the flange S0 of which is provided with dowels 51, radially spaced so as to be in register with the holes 36 in the flange 35 of the bush 34 of the sheath 14.

The fuse cartridge 37 is attached to the base of the sheath 14 by inserting the projecting spring ends of the terminal wires 40, 41 into the registering holes in the v insulation member 28 until contact is made with the adjacent ends of the terminal wires Z9, 30, when the rcspective 'flanges 35, Sil come into abutment and the dowels Si enter the registering holes 36, whereby the fuse cartridge 37 is securely held in position.

The charged fuse holder is then secured in operative positionby means of the union nut 33 which is screwed on to a correspondingly screw-threaded bush, not shown, through` which the fuse cartridge 37 projects into the space where the temperature is intended to be controlled.

It will be seen that the ypath of flow of the electric current is through the terminal 21, :terminal wires 29, dil, across the fuse 46, and via the terminal wires Ail, 3i? through the terminal 22.

When the predetermined temperature is reached, the fuse 456 melts and the resultant fracture of the 'fuse 46 causes the terminal wires di), 4l to spring apart, so breai ing the electric circuit.

The fuse cartridge 37 is then removed and a fresh fuse fitted, when the cartridge is replaced.

If desired, ready charged fuse cartridges may be held in reserve to facilitate speedy reinstatement.

ln the modification shown in Fig. 3, in which parts corresponding to those previously described are indicated by the same reference numerals distinguished by the addition of the exponent letter a, the insulation member 39 and the spring ended terminal wires fill, di are dispensed with, the insulation member 2%@ being extended to project into the sheath 33u and the terminal wires 29, 3i) also being extended so as to project in a continuous length through the insulation member 28a to a point ad jacent to the lower end of the sheath 382, where the ends of the terminal wires are sprung together and fitted with a fuse in the same manner as described with reference to Fig. l.

ln this case it will be necessary to remove the lower part. of the fuse holder in order to replace a fractured fuse.

l claim;

l. A thermal control fuse adapted for intercalation in an electric circuit, including a casing housing electrical terminals mounted in an insulation block in said casing, said casing being furnished with a removable cover and also with un attachable basal member provided with a tubular metal sheath, an insulation member located in said sheath having holes for the passage of two terminal Wires, the upper ends of which project into the aforesaid casing and are connected to the respective tcrminals,while the lower ends extend through the insulation member, a fue ther metal sheath connectible to the first-.mentioned sheath and housing continuations of the insulation member and the terminal wires, a distance piece in said second-mentioned sheath located between the underside of the in sulation member and an insert stop secured to the end oi said secondmentioned sheath, a fuse element secured across the ends of the terminal wires in such manner that the said terminal wires are held in tension whereby the said fuse clement is subjected to a predetermined tensilc stress, and means for securing the respective sheaths together.

2. A thermal control fuse as claimed in claim l, characterised in that the fuse element is maintained in a state of tension which may be adjusted to suit any fuse material, and is adapted to be fractured when subjected to a temperature within the solidus-liquidus range of the fuse material whereby to break the electric circuit, which temperature may be due to excessive electric current flowing through the circuit, or excessive external heat.

3. A thermal control vfuse as claimed in claim 1, having metal casing with a cover provided with an aperture for passage of electric lead wires, and furnished with :i metal having a flange adapted to form the base oli? the casing, also housing an insulation block secured to said ilange by screws and nuts, which also secure a metal plate to the top of said insulation block, including gaskets interposed respectively between the insulation block and the flange and between the insulationblocl;

and the metal plate, said metal plate being furnished with terminals secured thereto'but insulated therefrom, and having a central vertical pillar to which the aforesaid cover is secured, an insulation member or core located within the aforesaid metal sheath and provided with two holes for the passage of terminal wires, secured in electrical connection with the terminals by being clamped between the adjacent heads of the terminal bolts and washers strung on said bolts, the heads of said bolts being located in a recess in the base of the insulation block, the opposite ends of said terminal wires finishing a short distance from the end of the insulation member in the aforesaid sheath, a flanged bush furnished with an internally screw-threaded nut secured to the lower end ot said sheath as by welding whereby said nut is retained on said sheath. the flange being formed in its face with radially spaced holes, a detachable fuse cartridge or holder comprised of a cylindrical metal sheath provided at its upper end with an insulation membertted into the mouth of said second-mentioned sheath and having two holes therethrough to receive two terminal wires secured therein and which project beyond the upper face ot' the insulation member and are each reduced in diameter at their ends to provide attachment for small springs, the lower ends of the termina] wires projecting through the bottom of the insulation member to a point adjacent to the open end of the sheath, where the ends of the two terminal wires are drawn together and fastened in such position by a fuse, whereby due to their springy nature the terminal wires are held in tension and thc fuse element is subjected to a predetermined tensile stress, a liner secured in the cartridge sheath between the underside of the insulation member and a thiinble insert secured in the lower end of the said sheath as by welding, and a ilangcd bush secured to the upper end of said sheath and furnished with dowels radially spaced to register with'the holes in the flange of the bush of the first-mentioned sheath.

4. A thermal control fuse as claimed in claim 3, characterised in that the fuse cartridge is attached to the upper part of the fuse by inserting the ends of the terminal wires furnished with springs into the registering holes in the insulation member in the upper sheath until contact is made with the adjacent ends of the tirstnientioned terminal wires, the dowels entering the registering holes inthe ilange of the adjacent bush whereby the. fuse cartridge'is securely held in position.

5. A thermal control fuse as claimed in claim 3, further characterised in that the length of the extending portions of the terminal wiresin the fuse cartridge is determined by the degree of tension required to be exerted by the terminal wires on the fuse element when in tensed position.

6. A thermal control fuse as claimed in claim 3, further characterised in that when the predetermined temperature is reached either through excess of electric current or external heat, the fuse element melts, or its solidity disintegrates, the resultant fracture of the fuse causes the terminal `wires to spring apart, so breaking the electric circuit.

7. A thermal control fuse as claimed in claim 3, in which the insulation member of the upper sheath is lengthened to'extend into the fuse cartridge sheath, which is a pushv lit on said insulation member, Athe terminal wires projecting in a continuous length beyond the said insulation member to a point adjacent to the open end or" the fuse cartridge sheath where the ends of the ter minal wires are sprung together and litted with a fuse.

References Cited in the tile of this patent UNITED STATES PATENTS i474 New 

